Is there a possibility that there is an audience recording of Queen's concert in Portland 1977?

I think it would be a more than reasonable assumption that every Queen show starting with the Sheer Heart Attack tour (maybe barring exceptions for special cases like Tottenham Mayfair 12/19/79) was taped by at least one person in the audience.

Using Brussels 1974 as a sample size for instance, that's at minimum two tapers even in a crowd of only 500 or 600 (source 2 is long gone sadly). I've been researching concert taping as a phenomenon for years and have found that it was a far more common thing to do at that time than we will ever be able to realize. It wasn't something that required much intent, especially because of how relaxed concert security was in those days. Most people used their family's tabletop recorders with internal mics, recorded on cheap blanks, and then threw them into a drawer somewhere until they were either thrown out or preserved in some way.

Compared to other bands like Led Zeppelin, I believe the only reason why we don't have a flood of Queen audience tapes is because they weren't seen to be as "special"/worth collecting as a band like Zep or Pink Floyd, especially before Freddie died. As a result, they didn't catch the attention of old school traders tracking down every taper they could find. The average Queen taper was a vastly different person (and fan of music) than the average Zeppelin taper, and much less likely to be involved in things like tape trading and torrenting. Even the ones who were, in the case of Queen, sometimes heavily gatekept it, which is why so many UK recordings remained uncirculated until recent years (and many still are uncirculated!)

Likewise, what we have is mostly not a reflection of what was taped. It is far more indicative of who was trading, and even when things were traded, who traded more widely than others. The vast majority of Queen's shows in Detroit, for instance, exist as audience recordings, but seemingly weren't traded outside of Michigan.

I'm sure Portland 77 has a couple of audience tapes still around. It's just a question of if we're ever lucky enough that the person who has them realizes its value to Queen's history.